My newly added DDC macrobenchmarks tests have been timing out on the
test infra. It turns out that `headless` Chrome is significantly slower
than headful Chrome (reasons unknown, but perhaps related to hardware
acceleration). Using `--headless=new` instead of `flutter run`'s
headless flag (which uses the old headless mode) makes my local runs
significantly (10x+) faster.
*This time for sure*